In recent years, the communications industry has shown a growing interest in various types of wireless communications systems for communicating voice and/or data between numerous remote sites and a central location. It is well recognized that the use of a dedicated telephone facility for a conventional telephone system is not a convenient or economical option for all communications applications. For example, for many industrial applications, a central data collection site has a need for acquiring information from a variety of remotely located monitoring devices that collect data about the operation or performance of equipment. To overcome the limitations of the conventional telephone system, a two-way wireless communications link is often necessary to permit a response to a communication initiated from another location. In an attempt to solve the problem of supplying a response to an initial communication, the industry has offered various wireless communications systems, including two-way radios, cellular mobile radiotelephones, and paging systems.
To overcome the limitations of prior communications systems, the assignee for the present invention has developed a system for communicating data via a cellular network control channel of a cellular mobile radiotelephone (CMR) system. U.S. Pat. Nos. 5,526,401, 5,546,444, and 5,873,043, which are assigned to the assignee for the present application and contain subject matter fully incorporated herein by reference, describe an adapted use of the existing architecture of a CMR system in an efficient and cost-effective manner to support communications via the CMR system, including collection and reporting of data obtained at remote sites.
The data message system described in the referenced U.S. patents includes data reporting devices, at least one mobile switching center (MSC), and a data collection system connected directly or indirectly to the MSC or a Signal Transfer Point (STP). The MSC can issue commands or instructions, typically in a sequence of page messages, to the data reporting devices via the cellular network control channel of the CMR system. Each data reporting device can monitor the operation of a remote data source to collect selected data or can control the operation of a remote item in response to commands transmitted over the via the MSC. The data reporting device can transmit a data message containing the selected data via a cellular network control channel of the CMR system when the data reporting device first identifies itself or “registers” for operation with the MSC. Alternatively, the data reporting device can send the selected data via the cellular network control channel in a data message formatted to represent a “call origination” signal. In turn, the MSC can send the data message to the data collection system via a communications link. In this manner, the data message system takes advantage of an installed base of cellular communications equipment by using the cellular network control channel for data communications between a central location and one or more remote sites.
The data reporting device of the data message system typically communicates with the MSC via the reverse overhead control channel (RECC) of the cellular network control channel. In contrast, the MSC can communicate with a cellular-compatible device, such as a data reporting device, via the forward overhead control channel (FOCC) of the cellular network control channel. The conventional technique for sending a message to a cellular mobile radiotelephone from an MSC is the transmission of a page message over the FOCC. For example, a conventional cellular mobile radiotelephone can be stimulated by a transmission of the MSC to locate the mobile telephone unit when an incoming call from a landline has been placed to this unit. The data requirement for this type of trigger message is minimal for conventional cellular communications and, consequently, each message is independently processed as a complete data packet. This works well for the paging operations conducted by an MSC with conventional cellular mobile radiotelephones via the FOCC. However, this mechanism significantly limits the amount of information or instruction that can be provided by the MSC to a data reporting device via a page carried by the cellular network control channel. This is a disadvantage for applications requiring the communication of a commands and/or data via the CMR system to a remote cellular communications device for use by a controller, such as a programmable logic controller (PLC), coupled to a controllable item or instrument.
In view of the foregoing, there is a need for adapting the paging mechanism of a CMR system to support the transfer of commands and/or data for communications from an MSC to a cellular-compatible device. There is a further need for communicating with and controlling the operations of a remote controller, such as a PLC, coupled to a cellular-compatible device that can accept commands and/or data via the paging mechanism of a CMR system.